simone – despite your reference to an “ACT tribunal”, I’ll assume that you’re in NSW, and will advise as I have many times before, that a reliance on cooperation as an alternative to by-laws as the means to manage strata schemes’ affairs works well until just one person decides not to (cooperate).
That’s particularly critical when, as in your scheme’s situation, that failure to cooperate involves changes to the common property, to the appearance of the building, and leads to noise impacts upon neighbouring residents.
Your executive committee (E/C) has asked the owner concerned to relocate her air-conditioner, and as that’s been refused its best option in my opinion is to formally convene another meeting of members to vote on a motion to decide upon whether that owner is in breach of by-laws due to her causing damage to the common property (#5), altering the appearance of her lot (#17), and causing noise that interferes with the peaceful enjoyment of neighbours.
If the E/C’s reasonable belief is that any or all of those by-laws has been breached, then a vote should be taken to issue the owner with a Notice to comply for each of the by-laws that it believes have been breached (i.e. possibly 3 notices), and be prepared to substantiate that decision if the owner doesn’t comply and the matter proceeds to the NSW Civil & Administrative Tribunal (NCAT) over the issue of a penalty (for non-compliance).
Make sure that the E/C meeting is formally convened with an agenda comprising the suggested motions, and the it’s distributed in advance to all owners at least 72 hours in advance.
That’s the best option in my opinion given the circumstances, although your E/C could attempt mediation over the noise issues alone even though that’s a consequence of the breach, and therefore likely won’t address it as the prime issue.
The next priority is of course to place a motion on the agenda for the very next general meeting to create and register a special by-law covering owners’ installation of air-conditioners.